unit-i-computer-architecture.ppt -general studies

COMPUTER
ORGANIZATION AND
ARCHITECTURE

COMPUTER ORGANISATION
AND ARCHITECTURE
• The components from which computers are built,
i.e., computer organization.
• In contrast, computer architecture is the science
of integrating those components to achieve a
level of functionality and performance.
• It is as if computer organization examines the
lumber, bricks, nails, and other building material
• While computer architecture looks at the design
of the house.

UNIT-I INTRODUCTION
•Evolution of Computer Systems
•Computer Types
•Functional units
•Basic operational concepts
•Bus structures
•Memory location and addresses
•Memory operations
•Addressing modes
•Design of a computer system
•Instruction and instruction sequencing,
•RISC versus CISC.

INTRODUCTION
This chapter discusses the computer
hardware, software and their
interconnection, and it also discusses
concepts like computer types, evolution of
computers, functional units, basic
operations, RISC and CISC systems.

Brief History of Computer
Evolution
Two phases:
1. before VLSI 1945 – 1978
• ENIAC
• IAS
• IBM
• PDP-8
2. VLSI 1978  present day
• microprocessors !
VLSI = Very Large
Scale Integration

Evolution of Computers
FIRST GENERATION (1945 – 1955)
• Program and data reside in the same memory
(stored program concepts – John von Neumann)
• ALP was made used to write programs
• Vacuum tubes were used to implement the
functions (ALU & CU design)
• Magnetic core and magnetic tape storage
devices are used
• Using electronic vacuum tubes, as the switching
components

SECOND GENERATION (1955 –
1965)
• Transistor were used to design ALU & CU
• HLL is used (FORTRAN)
• To convert HLL to MLL compiler were used
• Separate I/O processor were developed to
operate in parallel with CPU, thus improving the
performance
• Invention of the transistor which was faster,
smaller and required considerably less power to
operate

• IC technology improved
• Improved IC technology helped in designing low cost,
high speed processor and memory modules
• Multiprogramming, pipelining concepts were
incorporated
• DOS allowed efficient and coordinate operation of
computer system with multiple users
• Cache and virtual memory concepts were developed
• More than one circuit on a single silicon chip became
available
THIRD GENERATION (1965-1975)

FOURTH GENERATION (1975-
1985)
• CPU – Termed as microprocessor
• INTEL, MOTOROLA, TEXAS,NATIONAL
semiconductors started developing
microprocessor
• Workstations, microprocessor (PC) & Notebook
computers were developed
• Interconnection of different computer for better
communication LAN,MAN,WAN
• Computational speed increased by 1000 times
• Specialized processors like Digital Signal
Processor were also developed

• E-Commerce, E- banking, home office
• ARM, AMD, INTEL, MOTOROLA
• High speed processor - GHz speed
• Because of submicron IC technology lot of
added features in small size
BEYOND THE FOURTH GENERATION
(1985 – TILL DATE)

COMPUTER TYPES
Computers are classified based on the
parameters like
• Speed of operation
• Cost
• Computational power
• Type of application

DESK TOP COMPUTER
• Processing &storage units, visual display &audio uits,
keyboards
• Storage media-Hard disks, CD-ROMs
• Eg: Personal computers which is used in homes and
offices
• Advantage: Cost effective, easy to operate, suitable for
general purpose educational or business application
NOTEBOOK COMPUTER
• Compact form of personal computer (laptop)
• Advantage is portability

WORK STATIONS
• More computational power than PC
•Costlier
•Used to solve complex problems which arises in
engineering application (graphics, CAD/CAM etc)
ENTERPRISE SYSTEM (MAINFRAME)
•More computational power
•Larger storage capacity
•Used for business data processing in large organization
•Commonly referred as servers or super computers

SERVER SYSTEM
• Supports large volumes of data which frequently need to
be accessed or to be modified
•Supports request response operation
SUPER COMPUTERS
•Faster than mainframes
•Helps in calculating large scale numerical and algorithm
calculation in short span of time
•Used for aircraft design and testing, military application
and weather forecasting

HANDHELD
• Also called a PDA (Personal
Digital Assistant).
• A computer that fits into a
pocket, runs on batteries,
and is used while holding
the unit in your hand.
• Typically used as an
appointment book, address
book, calculator, and
notepad.
• Can be synchronized with a
personal microcomputer as
a backup.

Basic Terminology
• Computer
– A device that accepts input,
processes data, stores data,
and produces output, all
according to a series of stored
instructions.
• Hardware
– Includes the electronic and
mechanical devices that
process the data; refers to the
computer as well as peripheral
devices.
• Software
– A computer program that tells
the computer how to perform
particular tasks.
• Network
– Two or more computers and
other devices that are
connected, for the purpose of
sharing data and programs.
• Peripheral devices
– Used to expand the
computer’s input, output and
storage capabilities.

Basic Terminology
• Input
– Whatever is put into a computer system.
• Data
– Refers to the symbols that represent facts, objects, or ideas.
• Information
– The results of the computer storing data as bits and bytes; the words,
numbers, sounds, and graphics.
• Output
– Consists of the processing results produced by a computer.
• Processing
– Manipulation of the data in many ways.
• Memory
– Area of the computer that temporarily holds data waiting to be processed,
stored, or output.
• Storage
– Area of the computer that holds data on a permanent basis when it is not
immediately needed for processing.

Basic Terminology
•Assembly language program (ALP) – Programs are written
using mnemonics
•Mnemonic – Instruction will be in the form of English like
form
•Assembler – is a software which converts ALP to MLL
(Machine Level Language)
•HLL (High Level Language) – Programs are written using
English like statements
•Compiler - Convert HLL to MLL, does this job by reading
source program at once

Basic Terminology
•Interpreter – Converts HLL to MLL, does this job
statement by statement
•System software – Program routines which aid the
user in the execution of programs eg: Assemblers,
Compilers
•Operating system – Collection of routines
responsible for controlling and coordinating all the
activities in a computer system

Calvin College
Computing Systems
Computers have two kinds of components:
• Hardware, consisting of its physical
devices (CPU, memory, bus, storage
devices, ...)
• Software, consisting of the programs it
has (Operating system, applications,
utilities, ...)

FUNCTIONAL UNITS OF COMPUTER
• Input Unit
• Output Unit
• Central processing Unit (ALU and Control Units)
• Memory
• Bus Structure

The Big Picture
Control
ALU
Memory
Processor
Input
Output
Since 1946 all computers have had 5 components!!!

Function
• ALL computer functions are:
– Data PROCESSING
– Data STORAGE
– Data MOVEMENT
– CONTROL
• NOTHING ELSE!
Data = Information
Coordinates How
Information is Used
IMPORTANT
SLIDE !

INPUT UNIT:
•Converts the external world data to a binary format, which
can be understood by CPU
•Eg: Keyboard, Mouse, Joystick etc
OUTPUT UNIT:
•Converts the binary format data to a format that a common
man can understand
•Eg: Monitor, Printer, LCD, LED etc

CPU
•The “brain” of the machine
•Responsible for carrying out computational task
•Contains ALU, CU, Registers
•ALU Performs Arithmetic and logical operations
•CU Provides control signals in accordance with some
timings which in turn controls the execution process
•Register Stores data and result and speeds up the
operation

Example
Add R1, R2
T1
T2
T3
T4
Enable R1
Enable R2
Enable ALU for addition operation
Enable out put of ALU to store result of the
operation

•Control unit works with
a reference signal called
processor clock
•Processor divides the
operations into basic
steps
•Each basic step is
executed in one clock
cycle
T1
T2
R1 R2
R2

MEMORY
•Stores data, results, programs
•Two class of storage
(i) Primary (ii) Secondary
•Two types are RAM or R/W memory and ROM read only memory
•ROM is used to store data and program which is not going to
change.
•Secondary storage is used for bulk storage or mass storage

Basic Operational Concepts
Basic Function of Computer
• To Execute a given task as per the appropriate
program
• Program consists of list of instructions stored in
memory

Interconnection between Processor and Memory

Registers
Registers are fast stand-alone storage locations that hold data
temporarily. Multiple registers are needed to facilitate the
operation of the CPU. Some of these registers are
 Two registers-MAR (Memory Address Register) and
MDR (Memory Data Register) : To handle the data
transfer between main memory and processor. MAR-
Holds addresses, MDR-Holds data
 Instruction register (IR) : Hold the Instructions that is
currently being executed
 Program counter: Points to the next instructions that is
to be fetched from memory

•(PC) (MAR)( the contents
of PC transferred to MAR)
•(MAR) (Address bus) Select a
particular memory location
•Issues RD control signals
•Reads instruction present in memory
and loaded into MDR
•Will be placed in IR (Contents
transferred from MDR to IR)

•Instruction present in IR will be decoded by
which processor understand what operation it
has to perform
•Increments the contents of PC by 1, so that it
points to the next instruction address
•If data required for operation is available in
register, it performs the operation
•If data is present in memory following
sequence is performed

•Address of the data MAR
•MAR Address bus select memory
location where is issued RD signal
•Reads data via data bus MDR
•From MDR data can be directly routed to ALU
or it can be placed in register and then
operation can be performed
•Results of the operation can be directed
towards output device, memory or register
•Normal execution preempted (interrupt)

Interrupt
• An interrupt is a request from I/O device
for service by processor
• Processor provides requested service by
executing interrupt service routine (ISR)
• Contents of PC, general registers, and
some control information are stored in
memory .
• When ISR completed, processor restored,
so that interrupted program may continue

BUS STRUCTURE
Connecting CPU and memory
The CPU and memory are normally connected by three
groups of connections, each called a bus: data bus, address
bus and control bus
Connecting CPU and memory using three buses

BUS STRUCTURE
•Group of wires which carries information form CPU to peripherals or
vice – versa
•Single bus structure: Common bus used to communicate between
peripherals and microprocessor
SINGLE BUS STRUCTURE
INPUT MEMORY PROCESSOR OUTPUT

Continued:-
• To improve performance multibus structure can be
used
•In two – bus structure : One bus can be used to fetch
instruction other can be used to fetch data, required
for execution.
•Thus improving the performance ,but cost increases

A2
A1
A0
Selected
location
0 0 0 0th
Location
0 0 1 1st
Location
0 1 0
0 1 1
1 0 0
1 0 1
1 1 0
1 1 1
D0
D0 D7 D7
PROCESSOR
RD
CS
W/R
A0
A1
A2
CONTROL BUS
ADDRESS BUS
DATA BUS

Cont:-
•23
= 8 i.e. 3 address line is required to select 8
location
•In general 2x
= n where x number of address lines
(address bit) and n is number of location
•Address bus : unidirectional : group of wires
which carries address information bits form
processor to peripherals (16,20,24 or more parallel
signal lines)

Cont:-
•Databus: bidirectional : group of wires which
carries data information bit form processor to
peripherals and vice – versa
•Controlbus: bidirectional: group of wires
which carries control signals form processor to
peripherals and vice – versa
•Figure below shows address, data and control
bus and their connection with peripheral and
microprocessor

Single bus structure showing the details of connection

PERFORMANCE
•Time taken by the system to execute a program
•Parameters which influence the performance are
•Clock speed
•Type and number of instructions available
•Average time required to execute an instruction
•Memory access time
•Power dissipation in the system
•Number of I/O devices and types of I/O devices
connected
•The data transfer capacity of the bus

MEMORY LOCATIONS AND ADDRESSES
MEMORY LOCATIONS AND ADDRESSES
•Main memory
Main memory is the second major subsystem in a
is the second major subsystem in a
computer. It consists of a collection of storage locations,
computer. It consists of a collection of storage locations,
each with a unique identifier, called an
each with a unique identifier, called an address
address.
.
•Data is transferred to and from memory in groups of
Data is transferred to and from memory in groups of
bits called
bits called words
words. A word can be a group of 8 bits, 16
. A word can be a group of 8 bits, 16
bits, 32 bits or 64 bits (and growing).
bits, 32 bits or 64 bits (and growing).
•If the word is 8 bits, it is referred to as a
If the word is 8 bits, it is referred to as a byte
byte. The term
. The term
“byte” is so common in computer science that
“byte” is so common in computer science that
sometimes a 16-bit word is referred to as a 2-byte word,
sometimes a 16-bit word is referred to as a 2-byte word,
or a 32-bit word is referred to as a 4-byte word.
or a 32-bit word is referred to as a 4-byte word.

Address space
•To access a word in memory requires an identifier.
Although programmers use a name to identify a word (or a
collection of words), at the hardware level each word is
identified by an address.
•The total number of uniquely identifiable locations in
memory is called the address space.
•For example, a memory with 64 kilobytes (16 address line
required) and a word size of 1 byte has an address space that
ranges from 0 to 65,535.

Memory addresses are defined using unsigned
binary integers.
i

Example 1
A computer has 32 MB (megabytes) of memory. How many bits
A computer has 32 MB (megabytes) of memory. How many bits
are needed to address any single byte in memory?
are needed to address any single byte in memory?
Solution
Solution
The memory address space is 32 MB, or 2
The memory address space is 32 MB, or 225
25
(2
(25
5
× 2
× 220
20
). This
). This
means that we need log
means that we need log2
2 2
225
25
, or
, or 25 bits
25 bits, to address each byte.
, to address each byte.
Example 2
A computer has 128 MB of memory. Each word in this computer
A computer has 128 MB of memory. Each word in this computer
is eight bytes. How many bits are needed to address any single
is eight bytes. How many bits are needed to address any single
word in memory?
word in memory?
Solution
Solution
The memory address space is 128 MB, which means 2
The memory address space is 128 MB, which means 227
27
.
.
However, each word is eight (2
However, each word is eight (23
3
) bytes, which means that we
) bytes, which means that we
have 2
have 224
24
words. This means that we need log
words. This means that we need log2
2 2
224
24
, or
, or 24 bits
24 bits, to
, to
address each word.
address each word.

Assignment of byte addresses
• Little Endian (e.g., in DEC, Intel)
» low order byte stored at lowest address
» byte0 byte1 byte2 byte3
• Eg: 46,78,96,54 (32 bit data)
• H BYTE L BYTE
• 8000
• 8001
• 8002
• 8003
• 8004
54
96
78
46
|

Big Endian
• Big Endian (e.g., in IBM, Motorolla, Sun,
HP)
» high order byte stored at lowest address
» byte3 byte2 byte1 byte0
• Programmers/protocols should be careful
when transferring binary data between Big
Endian and Little Endian machines

• In case of 16 bit data, aligned words begin at
byte addresses of 0,2,4,
………………………….
byte address of 0,4,8,………………………….
byte addresses of 0,8,16,
………………………..
• In some cases words can start at an arbitrary
byte address also then, we say that word
locations are unaligned

MEMORY OPERATIONS
• Today,
Today, general-purpose computers
general-purpose computers use a set of instructions
use a set of instructions
called a
called a program
program to process data.
to process data.
• A computer executes the program to create output data from input
A computer executes the program to create output data from input
data
data
• Both program instructions and data operands are stored in memory
• Two basic operations requires in memory access
• Load operation (Read or Fetch)-Contents of specified
memory location are read by processor
• Store operation (Write)- Data from the processor is stored in
specified memory location

• INSTRUCTION SET ARCHITECTURE:-
Complete instruction set of the processor
• BASIC 4 TYPES OF OPERATION:-
• Data transfer between memory and
processor register
• Arithmetic and logic operation
• Program sequencing and control
• I/O transfer

Register transfer notation (RTN)
Transfer between processor registers & memory,
between processor register & I/O devices
Memory locations, registers and I/O register names
are identified by a symbolic name in uppercase
alphabets
• LOC,PLACE,MEM are the address of memory
location
• R1 , R2,… are processor registers
• DATA_IN, DATA_OUT are I/O registers

•Contents of location is indicated by using square
brackets [ ]
•RHS of RTN always denotes a values, and is
called Source
•LHS of RTN always denotes a symbolic name
where value is to be stored and is called destination
•Source contents are not modified
•Destination contents are overwritten

Examples of RTN statements
• R2 [LOCN]
• R4 [R3] +[R2]

ASSEMBLY LANGUAGE
NOTATION (ALN)
• RTN is easy to understand and but
cannot be used to represent machine
instructions
• Mnemonics can be converted to machine
language, which processor understands
using assembler
Eg:
1. MOVE LOCN, R2
2. ADD R3, R2, R4

TYPE OF INSTRUCTION
Three address instruction
•Syntax: Operation source 1, source 2, destination
•Eg: ADD D,E,F where D,E,F are memory
location
•Advantage: Single instruction can perform the
complete operation
•Disadvantage : Instruction code will be too large to
fit in one word location in memory

TWO ADDRESS INSTRUCTION
•Syntax : Operation source, destination
•Eg: MOVE E,F MOVE D,F
ADD D,F OR ADD E,F
Perform ADD A,B,C using 2 instructions
MOVE B,C
ADD A,C
Disadvantage: Single instruction is not sufficient to
perform the entire operation.

ONE ADDRESS INSTRUCTION
• Syntax- Operation source/destination
• In this type either a source or destination
operand is mentioned in the instruction
• Other operand is implied to be a
processor register called Accumulator
• Eg: ADD B (general)
• Load D; ACC [memlocation _D]
• ADD E; ACC (ACC) +(E)
• STORE F; memlocation_ F (ACC )

Zero address instruction
• Location of all operands are defined
implicitly
• Operands are stored in a structure called
pushdown stack

Continued
 If processor supports ALU operations one data in memory
and other in register then the instruction sequence is
• MOVE D, Ri
• ADD E, Ri
• MOVE Ri, F
 If processor supports ALU operations only with registers
then one has to follow the instruction sequence given
below
• LOAD D, Ri
• LOAD E, Rj
• ADD Ri, Rj
• MOVE Rj, F

Basic Instruction Cycle
• Basic computer operation cycle
– Fetch the instruction from memory into a
control register (PC)
– Decode the instruction
– Locate the operands used by the instruction
– Fetch operands from memory (if necessary)
– Execute the operation in processor registers
– Store the results in the proper place
– Go back to step 1 to fetch the next instruction

INSTRUCTION EXECUTION & STRIAGHT LINE
SEQUENCING
Move A,R0
Add B,R0
Move R0,C
.
.
.
.
.
.
.
.
Contents
A
B
C
Data for Program
C [A]+[B]
}3-instruction program
segment
Address
Begin execution here i
i+4
i+8

• PC – Program counter: hold the address of the next
instruction to be executed
• Straight line sequencing: If fetching and executing of
instructions is carried out one by one from successive
addresses of memory, it is called straight line
sequencing.
• Major two phase of instruction execution
• Instruction fetch phase: Instruction is fetched form
memory and is placed in instruction register IR
• Instruction execute phase: Contents of IR is decoded
and processor carries out the operation either by
reading data from memory or registers.

BRANCHING
A straight line program for adding n
numbers
Using a loop to add n numbers

BRANCHING
• Branch instruction are those which changes the
normal sequence of execution.
• Sequence can be changed either conditionally or
unconditionally.
• Accordingly we have conditional branch instructions
and unconditional branch instruction.
• Conditional branch instruction changes the
sequence only when certain conditions are met.
• Unconditional branch instruction changes the
sequence of execution irrespective of condition of
the results.

CONDITION CODES
 CONDITIONAL CODE FLAGS: The processor keeps
track of information about the results of various
operations for use by subsequent conditional branch
instructions
• N – Negative 1 if results are Negative
0 if results are Positive
• Z – Zero 1 if results are Zero
0 if results are Non zero
• V – Overflow 1 if arithmetic overflow occurs
0 non overflow occurs
• C – Carry 1 if carry and from MSB bit
0 if there is no carry from MSB bit

Figure Format and different instruction types

Processing the instructions
Simple computer, like most computers, uses machine cycles.
A cycle is made of three phases: fetch, decode and execute.
During the fetch phase, the instruction whose address is determined by
the PC is obtained from the memory and loaded into the IR. The PC is
then incremented to point to the next instruction.
During the decode phase, the instruction in IR is decoded and the
required operands are fetched from the register or from memory.
During the execute phase, the instruction is executed and the results are
placed in the appropriate memory location or the register.
Once the third phase is completed, the control unit starts the cycle again,
but now the PC is pointing to the next instruction.
The process continues until the CPU reaches a HALT instruction.

Types of Addressing Modes
The different ways in which the location of the operand is
specified in an instruction are referred to as addressing
modes
• Immediate Addressing
• Direct Addressing
• Indirect Addressing
• Register Addressing
• Register Indirect Addressing
• Relative Addressing
• Indexed Addressing

Immediate Addressing
• Operand is given explicitly in the instruction
• Operand = Value
• e.g. ADD 5
– Add 5 to contents of accumulator
– 5 is operand
• No memory reference to fetch data
• Fast
• Limited range
Instruction
opcode
operand

Direct Addressing
• Address field contains address of operand
• Effective address (EA) = address field (A)
• e.g. ADD A
– Add contents of cell A to accumulator
– Look in memory at address A for operand
• Single memory reference to access data
• No additional calculations to work out effective
address
• Limited address space

Direct Addressing Diagram
Address A
Opcode
Instruction
Memory
Operand

Indirect Addressing (1)
• Memory cell pointed to by address field
contains the address of (pointer to) the
operand
• EA = [A]
– Look in A, find address (A) and look there for
operand
• e.g. ADD (A)
– Add contents of cell pointed to by contents of
A to accumulator

Indirect Addressing (2)
• Large address space
• 2n
where n = word length
• May be nested, multilevel, cascaded
– e.g. EA = (((A)))
• Draw the diagram yourself
• Multiple memory accesses to find operand
• Hence slower

Indirect Addressing Diagram
Address A
Opcode
Instruction
Memory
Operand
Pointer to operand

Register Addressing (1)
• Operand is held in register named in
address field
• EA = R
• Limited number of registers
• Very small address field needed
– Shorter instructions
– Faster instruction fetch

Register Addressing (2)
• No memory access
• Very fast execution
• Very limited address space
• Multiple registers helps performance
– Requires good assembly programming or compiler
writing

Register Addressing Diagram
Register Address R
Opcode
Instruction
Registers
Operand

Register Indirect Addressing
• C.f. indirect addressing
• EA = [R]
• Operand is in memory cell pointed to by
contents of register R
• Large address space (2n
)
• One fewer memory access than indirect
addressing

Register Indirect Addressing Diagram
Register Address R
Opcode
Instruction
Memory
Operand
Pointer to Operand
Registers

Indexed Addressing
• EA = X + [R]
• Address field hold two values
– X = constant value (offset)
– R = register that holds address of memory
locations
– or vice versa
 (Offset given as constant or in the index register)
Add 20(R1),R2 or Add 1000(R1),R2

Indexed Addressing Diagram
Register R
Opcode
Instruction
Memory
Operand
Pointer to Operand
Registers
Constant Value
+

Relative Addressing
• A version of displacement addressing
• R = Program counter, PC
• EA = X + (PC)
• i.e. get operand from X bytes away from
current location pointed to by PC
• c.f locality of reference & cache usage

Auto increment mode
• The effective address of the operand is the
contents of a register specified in the
instruction.
• After accessing the operand, the contents of
this register are automatically incremented to
point to the next item in the list
• EA=[Ri]; Increment Ri ---- (Ri)+
Eg: Add (R2)+,R0

Auto decrement mode
• The contents of a register specified in the
instruction are first automatically
decremented and are then used as the
effective address of the operand
• Decrement Ri; EA= [Ri] ----- -(Ri)

Addressing Architecture
• Memory-to-Memory architecture
– All of the access of addressing -> Memory
– Have only control registers such PC
– Too many memory accesses
• Register-to-Register architecture
– Allow only one memory address
• “load”, “store” instructions
• Register-to-Memory architecture
– Program lengths and # of memory accesses tend to be
intermediate between the above two architectures
• Single accumulator architecture
– Have no register profile
– Too many memory accesses
• Stack architecture
– Data manipulation instructions use no address.
– Too many memory (stack) accesses
– Useful for rapid interpretation of high-level lang. programs in which
the intermediate code representation uses stack operations.

Addressing Modes
• Implied mode
–The operand is specified implicitly in the
definition of the opcode.
• Immediate mode
–The actual operand is specified in the
instruction itself.

Addressing Modes (Summary)
Base register LDA #ADRS(R1) ACC <- M[R1+ADRS]

Instruction Set Architecture
• RISC (Reduced Instruction Set Computer) Architectures
– Memory accesses are restricted to load and store instruction,
and data manipulation instructions are register to register.
– Addressing modes are limited in number.
– Instruction formats are all of the same length.
– Instructions perform elementary operations
• CISC (Complex Instruction Set Computer) Architectures
– Memory access is directly available to most types of
instruction.
– Addressing mode are substantial in number.
– Instruction formats are of different lengths.
– Instructions perform both elementary and complex
operations.

Instruction Set Architecture
• RISC (Reduced Instruction Set Computer)
Architectures
– Large register file
– Control unit: simple and hardwired
– pipelining
• CISC (Complex Instruction Set Computer)
Architectures
– Register file: smaller than in a RISC
– Control unit: often micro-programmed
– Current trend
• CISC operation  a sequence of RISC-like operations

CISC Examples
• Examples of CISC processors are the
– System/360(excluding the 'scientific' Model
44),
– VAX,
– PDP-11,
– Motorola 68000 family
– Intel x86 architecture based processors.

Pro’s
• Emphasis on hardware
• Includes multi-clock complex instructions
• Memory-to-memory:
"LOAD" and "STORE"
incorporated in instructions
• Small code sizes,
high cycles per second
• Transistors used for storing
complex instructions

Con’s
• That is, the incorporation of older instruction sets
into new generations of processors tended to
force growing complexity.
• Many specialized CISC instructions were not
used frequently enough to justify their existence.
• Because each CISC command must be
translated by the processor into tens or even
hundreds of lines of microcode, it tends to run
slower than an equivalent series of simpler
commands that do not require so much
translation.

RISC Examples
• Apple iPods (custom ARM7TDMI SoC)
• Apple iPhone (Samsung ARM1176JZF)
• Palm and PocketPC PDAs and smartphones
(Intel XScale family, Samsung SC32442 -
ARM9)
• Nintendo Game Boy Advance (ARM7)
• Nintendo DS (ARM7, ARM9)
• Sony Network Walkman (Sony in-house ARM
based chip)
• Some Nokia and Sony Ericsson mobile phones

Pro’s
• Emphasis on software
• Single-clock,
reduced instruction only
• Register to register:
"LOAD" and "STORE"
are independent instructions
• Low cycles per second,
large code sizes
• Spends more transistors
on memory registers

Performance
• The CISC approach attempts to
minimize the number of instructions
per program, sacrificing the number
of cycles per instruction. RISC does
the opposite, reducing the cycles per
instruction at the cost of the number
of instructions per program.

Characteristics of RISC Vs CISC
processors
No RISC CISC
1 Simple instructions taking one
cycle
Complex instructions taking
multiple cycles
2 Instructions are executed by
hardwired control unit
Instructions are executed by
microprogramed control unit
3 Few instructions Many instructions
4 Fixed format instructions Variable format instructions
5 Few addressing mode, and most
instructions have register to
register addressing mode
Many addressing modes
6 Multiple register set Single register set
7 Highly pipelined Not pipelined or less pipelined

SUMMARY
Computer components and its function
Evolution and types of computer
Instruction and instruction sequencing
Addressing modes
RISC Vs CISC

REFERENCES
• Carl Hammacher,”Computer
Organization,”Fifth Edition,McGrawHill
International Edition,2002
• P.Pal Chaudhuri,”Compter Organization
and Design”,2nd
Edition ,PHI,2003
• William Stallings,”Computer organization
and Architecture-Designing for
Performance”,PHI,2004

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